The prostate is critically dependent on androgen receptor (AR) signaling for all aspects of its growth, as well as all stages of carcinogenesis. Indeed, androgen-deprivation therapy remains the most prevalent treatment for men with advanced prostate cancer. However, androgen-deprivation ultimately results in the emergence of "androgen-independent" (or hormone-refractory) disease, which counter-intuitively continues to rely on AR signaling despite the fact that androgens are absent or at least limiting. We have been investigating androgen-independence in a mutant mouse model based on the loss-of-function of two genes that are important for human prostate cancer, namely, the Nkx3.1 homeobox gene and the Pten tumor suppressor. These Nkx3.1;Pten mutant mice recapitulate stages of prostate tumorigenesis as occur in humans, including PIN, adenocarcinoma, and metastatic disease and the molecular pathways of cancer progression are partially conserved with the human disease. Most relevant for this proposal, androgen-deprivation of these mutant mice leads to androgen-independent phenotypes, which are evident from the survival and proliferation of the prostatic epithelium and the occurrence of high-grade PIN and/or cancer lesions following castration. Importantly, androgen-independent lesions of the Nkx3.1;Pten mutant mice have wild-type AR and require AR signaling, as is frequently the case for hormone refractory prostate cancer in humans. We propose to utilize these Nkx3.1;Pten mutant mice and their derivative cell lines to pursue the following Aims: Aim 1: Based on our previous findings showing that constitutive activation of Akt and Erk MAP kinase signaling act additively in culture and synergistically in vivo to promote androgen-independence, we will investigate the individual and collaborative roles of the Akt and B-Raf/Erk signaling pathways for androgen-independence by integrating studies in established cell lines and primary prostate tissues in culture and in vivo, and with validation to human prostate cancer. Aim 2: Based on our gene expression profiling analyses of cancer progression in Nkx3.1;Pten mutant mice, we will identify novel genes that are de-regulated in the mutant mice and investigate their relevance for hormone refractory prostate cancer in humans. Aim 3: Based on our recent generation of an inducible model system to achieve stochastic gene deletion specifically in the prostate epithelium, we will develop a "next-generation" mutant mouse model to investigate the evolution of androgen-independence and relevant signaling pathways in vivo. Relevance: Currently, patients with advanced prostate cancer have limited treatment options, the most effective being androgen-ablation therapy. However, this is only a temporary solution since hormone deprivation inevitably leads to the emergence of androgen-independent disease, which is highly aggressive, metastatic, and ultimately lethal. Therefore, it is of the utmost clinical significance to understand the evolution of androgen-independent prostate cancer and to delineate the underlying molecular pathways.